Field of the Invention
The present invention relates to a radiation imaging apparatus and a radiation detection system.
Description of the Related Art
As an imaging apparatus used for medical imaging diagnosis or nondestructive inspection by X-rays, a radiation imaging apparatus has been put to practical use, which uses a matrix substrate including a pixel array formed by combining switch elements such as TFTs (Thin Film Transistors) and conversion elements such as photoelectric conversion elements. Such a radiation imaging apparatus often performs an imaging operation in synchronism with radiation irradiation by a radiation generator. Synchronization is done mainly at two timings. The first timing is the timing of detecting radiation irradiation by the radiation generator and the start of the accumulation operation of the radiation imaging apparatus. Japanese Patent Laid-Open No. 2012-15913 discloses a radiation detection element capable of detecting the presence/absence of radiation irradiation without using a synchronization signal. When notified of change to the imaging mode, the radiation imaging apparatus transits from a standby state to a radiation detection wait state and determines the presence/absence of radiation irradiation.
The second timing is the timing of generating a radiation irradiation stop instruction to the radiation generator corresponding to the cumulative exposure dose of radiation from the radiation generator to a sensor. A device configured to do synchronization with these timings is called AEC (Automatic Exposure Control) that controls a radiation transmission dose. Japanese Patent Laid-Open No. 2006-334154 discloses correcting a radiation dose using signals from the pixels of an ROI (Region Of Interest) obtained by fluorography to attain a clear X-ray image.
To detect the start of irradiation of radiation from the radiation generator, it is necessary to continuously monitor the signal from the radiation detection element, as described in Japanese Patent Laid-Open No. 2012-15913. More specifically, to detect the signal output from the radiation detection element, the circuit used to determine the presence/absence of radiation irradiation needs to be continuously operated for a time of several sec to several min. In addition, to detect the radiation exposure dose (radiation dose) in the region of interest (ROI), processing needs to be performed for each ROI, as described in Japanese Patent Laid-Open No. 2006-334154. In a case where a single detection element serves as the detection element for detecting the presence/absence of radiation irradiation and the detection element for detecting the radiation exposure dose in the ROI, if the arrangement of detection elements is optimized to determine the presence/absence of radiation irradiation, the spatial resolution may be short when detecting the radiation dose. On the other hand, if the arrangement of detection elements is optimized to determine the radiation dose, the number of ROIs increases, and the outputs from the detection elements disperse for each ROI, and it may be impossible to sufficiently obtain a signal level to determine the start of radiation irradiation.